The percentage voltage regulation of transmission lines is computed as:

(Where s is the sending end; R, receiving end; NL, no-load; FL, full-load)

Concept:

Voltage regulation of Transmission line:​

• When a transmission line is carrying a current, there is a voltage drop in the line due to the resistance and inductance of the transmission line.
• Finally, the receiving end voltage ( VR ) of the line is generally less than the sending end voltage (VS)
• The difference in voltage at the receiving end of the transmission line between the conditions of no-load and the full load is called voltage regulation
• Voltage regulation is expressed as a percentage of the receiving end voltage.

 \(V.R =\frac{V_S - V_R}{V_R} \times 100=\frac{{\left| {V_R^{NL}} \right| - \left| {{\rm{V}}_{\rm{R}}^{{\rm{FL}}}} \right|}}{{\left| {{\rm{V}}_{\rm{R}}^{{\rm{FL}}}} \right|}} \times 100\)

Note: At no load, \(|V_S|=|V_R|\)